"When a new Japanese soldier would come, they raped all three of us. They took turns, sometimes once or twice a day. I was so weak I couldn't take it. I was only 14 years old," said Grandma Adela in The Apology.

It took filmmaker Tiffany Hsiung five years to persuade three former "comfort women," profiled in the documentary The Apology, to give unflinching and painful testimony about their experiences being forced into sexual slavery during World War II.

"The war hasn't ended for any of the survivors. And that's what I was really interested in documenting," said Hsiung.

Her film won Best Documentary award at the Busan International Film Festival in South Korea last year, and this week will be featured at the Human Rights Watch Film Festival in New York City.

The Apology focuses on the lives of Grandma Adela in the Philippines, Grandma Gil in South Korea, and Grandma Cao in China, who were among the reported 200,000 girls and young women across Asia, known as "comfort women," that were allegedly kidnapped by the Japanese army, imprisoned in military run brothels known as "comfort stations," and forced into prostitution, abused and raped.

Watch the preview for 'The Apology'

Historical divide

The extent of Japanese wartime atrocities committed in Asia continues to be a contentious and politically charged issue. During the administration of Japanese Prime Minister Shinzo Abe, some of his nationalist supporters have attempted to downplay past Japanese war crimes in history textbooks and even suggested the "comfort women" volunteered to work as prostitutes and were not coerced.

For over 20 years, surviving "comfort women" and activist supporters in South Korea have conducted weekly protests in front of the Japanese Embassy in Seoul to demand an official public apology that specifically articulates the Japanese government's responsibility for perpetrating these wartime atrocities, and they want official state compensation made to the victims.

A 2015 "comfort women" deal between former South Korean President Park Geun-hye Seoul and Prime Minister Abe had agreed to resolve all grievances, but both the "comfort women" and current President Moon Jae-in have rejected the carefully worded statement of apology by Abe and the $8 million Tokyo donation to a victims fund as too vague and insincere.

Acknowledging truth

Grandma Gil, one of the South Korean "comfort woman" featured in The Apology, is a leading activist seeking justice for the survivors. In the film she travels to Japan on a speaking tour, where she is harassed by conservative protesters calling her a prostitute, but also embraced by teenage girls at a Japanese school who were brought to tears by her story.

"For over 70 years I have not lived like a normal person. Would the wound go away if you apologize? No. The scars will remain but my heart can heal. I am waiting for that day," Grandma Gil told the Japanese students.

On the 70th anniversary of the end of World War II, Prime Minister Abe expressed "sincere condolences' to victims of Japan's past military aggression, but he also emphasized that "generations not involved in the conflict should not be burdened with continued apologies."

Hsiung said her documentary is not an attempt to place guilt on endless generations of Japanese but to acknowledge the truth and learn from the past.

"Just because everyone who has been responsible for that, and committed that, have all passed away, it doesn't mean that that history and those atrocities get lost," she said.

The Apology also contrasts the outspoken network for South Korean "comfort women" with the lack of support and isolation for the survivors in China and the Philippines. China's restrictive political environment in particular has made it difficult for "comfort women" supporters to organize.

Hsiung said during the filming of the documentary she became a conduit connecting "comfort women" survivors to the wider movement. In one scene in the film Grandma Adela is encouraged to speak out when she watches video of a "comfort women" rally in Seoul.

"I think when people get to see that they are not alone, it is not an isolated issue, it's not just in their village, it's not just this one grandmother, when they see that it is part of a bigger thing, they feel more inclined to participate," said Hsiung.